This invention relates to foamed, modified polypropylene resin particles useful for molding a foamed, molded article and to a method of preparing same.
Foamed polypropylene particles are now utilized for molding foamed, molded articles because of high heat resistance and high stiffness thereof. To improve the rigidity of such molded articles, it is proposed to graft styrene to polypropylene resin.
JP-B-59-40164 discloses foamed, crosslinked polypropylene resin particles composed of 70% by weight of a polypropylene resin and 30% by weight of a polystyrene grafted to the polypropylene. Crosslinking is, however, not advantageous because the crosslinked resin cannot be regenerated or reused, because the use of a crosslinking agent invites an increase of costs and because the crosslinking requires an additional heating step.
JP-B-3-33186 discloses foamed, non-crosslinked polypropylene resin particles composed of 60% by weight of a polypropylene resin and 40% by weight of a polystyrene grafted to the polypropylene. The use of such a large amount of polystyrene, however, causes the lowering of the heat resistance and stiffness. Further, soot is apt to form when the molded product is burnt. The graft copolymer is prepared using 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane as a polymerization initiator.